Nov 1 (Reuters) - Tesoro Logistics LP on Friday said it is restarting the 20-year-old North Dakota pipeline that spilled 20,600 barrels of oil onto farmland in September after it secured permission from federal regulators.
The U.S. Department of Transportation's Pipeline and Hazardous Materials Safety Administration (PHMSA) had issued a safety order on Thursday, ordering Tesoro to make fixes on the pipeline and the larger North Dakota system of which it is a part.
A local farmer discovered the leak, the biggest in North Dakota since the oil boom took off a few years ago and the biggest spill on U.S. soil since an Exxon Mobil pipeline leaked 5,000 to 7,000 barrels of heavy Canadian crude in Mayflower, Arkansas last March.
There are no indications that corrosion or other defects led to the leak, Tesoro said in statement. Preliminary results of the investigation point to a small hole that was created by an electrical discharge, the company added.
"The source of the electrical current remains under investigation," Tesoro's statement reads in part.
The federal regulator echoed Tesoro's statements on the cause of the leak.
"Lightning could be the source, but the metallurgical examination will look at all possible factors that may have caused the failure," Damon Hill, a PHMSA spokesman said in an email.
A routine inspection had detected some anomalies on the pipeline a few days before the leak.
The ruptured pipeline runs 35 miles from Tioga to Black Slough in North Dakota. It was built by BP Plc BP.L in 1993.